1. Field of the Invention
The present invention relates to a method for determining a force at the hub of a wheel of a vehicle whilst traveling. More specifically, the invention relates to a method for measuring the forces at the hub generated by the wheel-road contact forces acting on the pneumatic tyre of a vehicle wheel whilst traveling. The invention also relates to a wheel for vehicles suitable for allowing said method to be carried out.
2. Description of the Related Art
Throughout the present description and in the subsequent claims, the expression: wheel-road contact forces, is used to indicate the stresses applied on the wheel by the road surface (or by a device which simulates the road surface, such as a rolling runway of a drum simulating the road surface). Such stresses include, for example, the vertical and/or longitudinal and/or lateral forces acting locally on the pneumatic tyre and/or the moments generated by such forces.
As known, in the field of the vehicle dynamic control, a substantial part of the research has as a primary purpose that of allowing the real time monitoring of the behavior of wheels whilst they are traveling. This is in order to contribute to ensuring dynamic control of the vehicle in the different conditions of use, for such a purpose suitably adjusting possible safety and/or comfort devices foreseen on the vehicle, such as ABS (Anti Block System), VDC (Vehicle Dynamic Control), suspension adjustment devices, steering adjustment devices, power adjustment devices and transmission adjustment devices. The real time monitoring of the wheels can also be useful for identifying the causes of accidents or other diagnostic and/or precautionary purposes.
For such a purpose, wheels and vehicles can be equipped with devices capable of detecting in real time information relative to the current dynamic conditions of the wheel whilst traveling. Such information is used on the same vehicle to suitably adjust the aforementioned safety and/or comfort devices so as to contribute to ensuring that the driver has the control of the vehicle in those specific conditions of use. The aforementioned information can also be stored or sent telematically to a remote control station to carry out a diagnostic analysis of the wheel.
Amongst the information considered of interest for achieving the aforementioned purposes there are those linked to the magnitude and distribution of the stresses applied by the road surface on the pneumatic tyre and the deformations of the wheels under a load.
For example, the information relative to the stresses acting on each pneumatic tyre and transmitted to the hub can be used to suitably adjust the braking force on each pneumatic tyre (for example through ABS). Such information can also be used to determine the dynamic stability of the vehicle and thus suitably adjusting the steering, when it is used to control the lateral dynamics. Moreover, such information can also be used to adjust the rigidity and behavior of the suspension system acting on each pneumatic tyre.
Devices and methods for the real time monitoring of the wheels of a vehicle through detection of the deformations of the rim due to stresses applied by the road surface to the pneumatic tyre are known.
For example, US 2003/0058118 A1 discloses a system for monitoring a pneumatic tyre of a vehicle, in which the deformation of a pneumatic tyre under a load is detected to obtain information linked to such a deformation, such as the load on the pneumatic tyre, the total mass of the vehicle and the mass distribution of the vehicle. The deformation of the pneumatic tyre is detected through detection of the variations in acceleration of the pneumatic tyre in rotation (by means of an acceleration sensor mounted on the pneumatic tyre, preferably on an inner surface of the tread) and generation of electric signals representing the variations in acceleration at the wheel-road contact zone. The Applicant has noted that the actuation of the method described in such a document requires the arrangement of an acceleration sensor inside the pneumatic tyre. Therefore, this is a detection system that is invasive on the pneumatic tyre and that thus necessarily provides useful results only for that specific pneumatic tyre on which the acceleration sensor is installed. Such a system also involves technical complications in the assembly of the wheel, whereas the addition of mass to the pneumatic tyre implies greater problems of uniformity, or else less comfort associated with irregular and greater wear.
Different devices and methods are known that foresee a measurement of the wheel-road contact forces through the use of strain gauges mounted on the wheel in positions other than the pneumatic tyre.
For example WO 03/008243 discloses a device for detecting the forces acting on a pneumatic tyre, such a device comprising a disc intended to be mounted between the hub and the rim of the wheel and provided with a plurality of strain gauges suitable for detecting the forces acting on the pneumatic tyre, and a detection portion suitable for determining an abnormality in the detection of the forces acting on the pneumatic tyre to allow a subsequent correction of such an abnormality.
U.S. Pat. No. 6,681,646 discloses a device for detecting the deformations of a wheel for a vehicle comprising a substantially annular element placed between the hub and the rim of the wheel and on which a plurality of strain gauges suitable for detecting the forces acting upon the pneumatic tyre are mounted.
The Applicant has noted that the devices described in the two prior art documents discussed above require the arrangement in the wheel of additional rotating masses on which the strain gauges are to be mounted. From this derives a technical complication in the assembly operations of the wheel, a significant increase in the overall weight of the wheel and an alteration of the dynamic behavior of the wheel itself.
The Applicant has considered the problem of determining in real time the forces at the hub of a wheel of a vehicle generated by the wheel-road contact stresses acting whilst traveling through a system for detecting deformations which, as well as allowing, through suitable algorithms, a reliable measurement of the actual stresses/forces at the hub generated by the contact between pneumatic tyre and road surface in the different conditions of use to be obtained, is non-invasive on the pneumatic tyre (so as to make the method able to be carried out irrespective of the specific type of pneumatic tyre mounted on the rim) and does not involve a significant increase in the overall weight of the wheel nor an alteration of the dynamic behavior of the wheel itself. The Applicant has thus verified that such a problem is solved by associating at least one deformation sensor directly on the rim of the wheel in at least one predetermined position and according to at least one predetermined orientation, so as to be able to detect, during travel, at least one deformation component of the rim of the wheel and then apply to said at least one deformation component a correlation parameter characteristic of that specific rim.